Tip effects in the scanning-tunneling microscopy of semiconductor electrodes (original) (raw)
Related papers
1990
The successful expansion which the scanning tunneling microscopy (STM) has had is dependent on its ability to examine surfaces on a sub-nanometric scale and on providing in situ (i.e. in the presence of bulk electrolyte) sample examination. In addition to the ability to study metals and semiconductors in vacua, the application of the technique to surfaces in contact with an electrolytic solution has prompted increased interest amongst electrochemists. We discuss herein the technique, with particular reference to advances in electrochemical applications. A new scanning tunneliig microscope for operation in electrolytic environments is described. Atomic force microscopy, scanning electrochemical microscopy and scanning ion-conducting microscopy are compared with the STM.
Scanning tunneling microscopy applications in electrochemistry—beyond imaging
Journal of Electroanalytical Chemistry, 2000
Scanning tunneling microscopy (STM) has gradually matured into a powerful tool for imaging electrode surfaces in the electrochemical environment with atomic resolution. It has been used to elucidate numerous old puzzling structural issues and to reveal many new interesting phenomena. As an imaging tool, it will continue to contribute to the understanding of various electrochemical processes on electrode surfaces. STM is more than an imaging tool for structural characterizations, other important electrochemical applications, such as probing electron transfer processes, fabricating nanostructures and studying fast electrochemical kinetics, have also been actively pursued. These later unconventional applications are the focus of this discussion.
Langmuir, 1998
The surface of a p-MoSe2 electrode has been observed in 0.05 M HNO3, in situ, by electrochemical scanning tunneling microscopy (ECSTM). Randomly oriented nanometer size spots have been observed on the surface. The STM images of the p-MoSe2 surface have been found to change with the electrode potential. That is, the nanometer size spots appeared as a dark contrast under a smaller band bending condition (0.2 V versus SCE) while the spots disappeared or further appeared as bright contrast under a larger band bending condition (0 and -0.2 V versus SCE). This is presumed to result from whether the acceptor level, within the band gap of the p-MoSe2, is occupied or not. In addition, it will depend on the electrode potential, which determines the amount of the band bending.
In situ scanning tunneling microscopy
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1990
The successful expansion which the scanning tunneling microscopy (STM) has had is dependent on its ability to examine surfaces on a sub-nanometric scale and on providing in situ (i.e. in the presence of bulk electrolyte) sample examination. In addition to the ability to study metals and semiconductors in vacua, the application of the technique to surfaces in contact with an electrolytic solution has prompted increased interest amongst electrochemists. We discuss herein the technique, with particular reference to advances in electrochemical applications. A new scanning tunneliig microscope for operation in electrolytic environments is described. Atomic force microscopy, scanning electrochemical microscopy and scanning ion-conducting microscopy are compared with the STM.
In Situ Study of Silver Electrodeposition at MoSe2 by Electrochemical Scanning Tunneling Microscopy
Langmuir, 1998
The electrodeposition of Ag at MoSe2 has been investigated, in situ, by electrochemical scanning tunneling microscopy (EC-STM). The process was investigated by observing MoSe2 at fixed electrode potentials which were referenced to the onset potential in the cyclic voltammograms of Ag electrodeposition at MoSe2. When an electrode potential more negative than the onset potential was applied to MoSe2, continuous Ag bulk deposition occurred. Consistently, the scanning tunneling microscopy (STM) image showed Ag deposits which exhibit a growth mode between island and layer growth. In the STM images taken near the onset potential, a small amount of Ag, presumably with sub-monolayer level coverage, was thought to be deposited. This initial deposition occurred so as to make the MoSe2 surface smooth in the STM images. STM imaging was difficult in the electrode potential region positive of the onset potential because the applied bias voltage became small. However, the STM images acquired during Ag deposition after applying such an electrode potential exhibited a characteristic morphological change, from which we infer that those processes were related to the MoSe2 reaction with Ag.
Electrostatic sample-tip interactions in the scanning tunneling microscope
Physical Review Letters, 1993
Local surface photovoltage (SPV) measurements were used to measure how the electric field of a scanning tunneling microscope tip perturbs the electronic band structure at Si(001), Si(111)-(7x 7), and H-terminated Si(111)surfaces. The results demonstrate that tip-induced band bending is important under typical STM conditions even on surfaces whose surface Fermi levels are nominally "pinned. ' Spatially resolved measurements of band bending as a function of sample bias show that atomic-scale contrast in SPV images can result from local variations in the ability of the surface states under the tip to screen external electric fields.
Tunneling tips imaged by scanning tunneling microscopy
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1990
Electrochemically etched tips commonly used for scanning tunneling microscopy (STM) have been investigated by STM itself. By appropriate positioning, the topography of the apex of the tips could be investigated, leading to a typical value for the tip radius of 300 nm. Different techniques have been attempted to untangle the convoluted STM image. By rotating one tip relative to the other, or by exchanging one tip and leaving the other in place, some distinct features can be attributed to the one or the other tip. Furthermore, the profile of the tip could be investigated by scanning over the edge of a cleaved crystal. Beside the fundamental interest in the tip structure itself, this configuration offers the unique feature of unambiguous relocation of the scanned area when the tip investigated in that experiment has been removed and reinstalled to the microscope.
Internal image potential in semiconductors: Effect on scanning tunneling microscopy
Physical Review B, 1993
The tunneling of electrons from a semiconductor surface to a metal tip, across a vacuum gap, is influenced by two image interactions: an attractive image potential in the vacuum region, which lowers the apparent tunneling barrier, and a repulsive image potential in the semiconductor interior, which raises it for conduction-band electrons. We report on detailed calculations of tunneling currents and apparent barrier heights for a model metal-vacuum-semiconductor junction which utilize semiclassical dielectric functions to compute the image potential in all three regions. The effect of image forces is found to be small compared to that of either the vacuum barrier or tip-induced band bending. In particular, the image-induced barrier in the semiconductor has only a minor influence on either the apparent barrier height or the shape of current-voltage characteristics, both of which are routinely measured in scanning-tunneling-microscopy experiments. This finding is explained by a qualitative WKB analysis and several simple arguments.
Surface science, 2005
Electrodes with an effective radius of about 10 nm have been produced by a combination of electrochemical etching, electrophoretic deposition of polymer, and heat curing. Their size and stability were characterized by cyclic voltammetry. They were then used in combined electrochemical scanning tunneling microscopic (ECSTM) and scanning electrochemical microscopic (SECM) experiments. In an extension of an earlier report, electrochemical surface modification approaches are reported here. They comprise the local electrochemical removal of a self-assembled monolayer (SAM) of dodecanethiol on flame-annealed gold by an electrochemical desorption procedure. The possibility of local electrochemical deposition is demonstrated by positioning a nanoelectrode 0.5 nm above a surface and switching off the distance regulation while performing an electrodeposition of Pt at the tip. The growing deposit bridges the tip-sample gap. If the distance regulation is switched on after 1 ms, the Pt junction is disrupted leaving a Pt nanodot at the sample surface. The dot was characterized by ECSTM experiments after solution exchange. Digital simulations by the boundary element method (BEM) provide a quantitative description of Faraday currents in nanoelectrochemical assemblies. A software tool was created that can accept arbitrary geometries as input data sets. The flexibility of the simulation strategy was demonstrated by the calculation of local current densities during electrochemical copper deposition on a 0039-6028/$ -see front matter Ó Surface Science 597 www.elsevier.com/locate/susc smooth electrode in the presence of an ECSTM tip close to the surface. The current densities deviate less than 1% from those in the absence of tip if the average current density is kept below 1 lA cm À2 . SECM approach curves for nanoelectrodes were also calculated.
Applied Physics A: Materials Science & Processing, 1998
The van-der-Waals surfaces (0001) of the layered structure semiconductors WS 2 and WSe 2 are known to be free of intrinsic surface states. Therefore, they provide an ideal system for investigations of the influence of individual dopants on the local electronic properties, which can be measured by scanning tunneling microscopy (STM). Individual dopant sites were resolved as topographic depressions superimposed on the atomically resolved lattice. The apparent depth of these depressions showed a discrete statistical distribution and was attributed to the spatial depth of the dopant site. Using an STM-induced electrochemical process, we could locally expose the first and second sub-surface layer to correlate the previously recorded topographic contrast to the location of buried dopants. To our knowledge this is the first direct proof of the capability of STM to detect individual sub-surface dopants. An interpretation of the contrast mechanism is given in terms of tip-induced band-bending effects and current transport mechanisms involving minority charge carrier injection and majority charge carrier extraction.